[PATCH v3 14/35] x86/bugs: Restructure bhi mitigation

David Kaplan
2025-01-08T20:25:48Z

Restructure bhi mitigation to use select/apply functions to create
consistent vulnerability handling.

Define new AUTO mitigation for bhi.

Signed-off-by: David Kaplan <david.kaplan@amd.com>
---
arch/x86/kernel/cpu/bugs.c | 19 +++++++++++++++----
1 file changed, 15 insertions(+), 4 deletions(-)

diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
index 849abdc0da91..fb92344d63cd 100644
--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -82,6 +82,8 @@ static void __init l1d_flush_select_mitigation(void);
static void __init srso_select_mitigation(void);
static void __init gds_select_mitigation(void);
static void __init gds_apply_mitigation(void);
+static void __init bhi_select_mitigation(void);
+static void __init bhi_apply_mitigation(void);

/* The base value of the SPEC_CTRL MSR without task-specific bits set */
u64 x86_spec_ctrl_base;
@@ -201,6 +203,7 @@ void __init cpu_select_mitigations(void)
*/
srso_select_mitigation();
gds_select_mitigation();
+ bhi_select_mitigation();

/*
* After mitigations are selected, some may need to update their
@@ -222,6 +225,7 @@ void __init cpu_select_mitigations(void)
rfds_apply_mitigation();
srbds_apply_mitigation();
gds_apply_mitigation();
+ bhi_apply_mitigation();
}

/*
@@ -1759,12 +1763,13 @@ static bool __init spec_ctrl_bhi_dis(void)

enum bhi_mitigations {
BHI_MITIGATION_OFF,
+ BHI_MITIGATION_AUTO,
BHI_MITIGATION_ON,
BHI_MITIGATION_VMEXIT_ONLY,
};

static enum bhi_mitigations bhi_mitigation __ro_after_init =
- IS_ENABLED(CONFIG_MITIGATION_SPECTRE_BHI) ? BHI_MITIGATION_ON : BHI_MITIGATION_OFF;
+ IS_ENABLED(CONFIG_MITIGATION_SPECTRE_BHI) ? BHI_MITIGATION_AUTO : BHI_MITIGATION_OFF;

static int __init spectre_bhi_parse_cmdline(char *str)
{
@@ -1785,6 +1790,15 @@ static int __init spectre_bhi_parse_cmdline(char *str)
early_param("spectre_bhi", spectre_bhi_parse_cmdline);

static void __init bhi_select_mitigation(void)
+{
+ if (!boot_cpu_has(X86_BUG_BHI) || cpu_mitigations_off())
+ bhi_mitigation = BHI_MITIGATION_OFF;
+
+ if (bhi_mitigation == BHI_MITIGATION_AUTO)
+ bhi_mitigation = BHI_MITIGATION_ON;
+}
+
+static void __init bhi_apply_mitigation(void)
{
if (bhi_mitigation == BHI_MITIGATION_OFF)
return;
@@ -1916,9 +1930,6 @@ static void __init spectre_v2_select_mitigation(void)
mode == SPECTRE_V2_RETPOLINE)
spec_ctrl_disable_kernel_rrsba();

- if (boot_cpu_has(X86_BUG_BHI))
- bhi_select_mitigation();
-
spectre_v2_enabled = mode;
pr_info("%s\n", spectre_v2_strings[mode]);

--
2.34.1